Experts in the field are familiar with various injectable implants. For example, silicon gels (or silicon oils) are well-known, but these gels have the inconvenience of not being biodegradable. Moreover, silicon is often the cause of chronic inflammation, granuloma formation and even delayed allergic reactions. Collagen suspensions have also been very widely used over the past ten years. However, collagen generally is of bovine origin, which is undesirable for health and generally subject to additional regulatory requirements. Attempts to re-implant fatty cells removed from the patients themselves are also reported. However, the duration of the filling effect is generally less than the patient would like.
Other implants have been used, comprising a gelatine or collagen solution including, in suspension, polymethyl methacrylate (PMMA) microspheres having a diameter of 20 to 40 μm. PMMA, however, is not biodegradable and the gelatine or collagen solution is generally derived from bovine sources.
EP 0 969 883 describes an implantable gel including L-PLA (polylactic acid) microspheres with a diameter of 20 to 40 μm suspended in a carboxy methylcellulose gel (CMC). This gel is injectable and can be supplied in a sterile syringe. This product shows an acceptable efficacy but may present poor syringability (clogging of the required low-diameter needles may be noted) and a biodegradability which is too slow for some of the desired applications. The particles have the tendency to aggregate in the packaging, in particular in a syringe, making injections difficult and leading to inconsistent results. Non-homogeneous distribution of the particles in the injection area may actually be observed in patients. The expected aesthetic result is therefore not achieved and areas overloaded with particles are noted, sometimes adjacent to areas free of particles. The very long resorption time of the PLA (having a high molecular weight) may be of several years, which may also lead to inflammatory reactions in the long run.
There is therefore a real need for new biomaterials which do not have the drawbacks of the prior art, and particularly biomaterials which are useful as immediate filler materials, able to generate fibrosis and also capable of being resorbed to avoid chronic inflammatory reactions or rejection in the long run.